Recently, the industry became interested in developing composite bonding technology for bonding various materials having different properties to each other to form a composite body.
Such bonding materials include metal beryllium, which is used for various purposes, such as transmission windows for X-ray, equipment due to excellent X-ray transmissibility and various applications related to nuclear equipment.
For applying to X-ray windows, it has been conventional practice to bond metal beryllium to a flange or like structural body made of stainless steel by brazing or diffusion bonding. However, stainless steel to which metal beryllium has been directly bonded suffers from a general problem of insufficient thermal conductivity.
Therefore, in order to improve thermal conductivity, a bonding process has been developed in which the copper alloy is bonded to a structural body of stainless steel in advance, and the metal beryllium is then bonded to the bonded body of copper alloy and stainless steel.
However, the above-mentioned bonding process requires that, after the stainless steel and copper alloy have been bonded to each other, an additional step is required to bond the metal beryllium to the bonded body of copper alloy and stainless steel by brazing or diffusion bonding, so that there remain problems that not only the bonding treatment is complicated, but also it is costly to perform.
Also, it has been a general practice that the brazing or diffusion bonding of metal beryllium be performed at a temperature within a range of 650 to 800.degree. C. This temperature range overlaps with the sensitizing temperature of the stainless steel. However, when brazing or diffusion bonding is performed in such a temperature range the corrosion resistance of the stainless steel is significantly diminished.